A leading oncologist said the findings will lead to a "fundamental change" in how the disease is treated.
More than 20,000 women in the United Kingdom are diagnosed with hormone-receptor positive, HER2-negative, node-negative breast cancer annually.
Baroness Delyth Morgna, chief executive of Breast Cancer Now, said: "We hope these practice-changing findings will now help refine our use of chemotherapy on the NHS".
The US team led by Dr Steven Rosenberg, from the National Cancer Institute in Bethesda, Maryland, identified immune system T-cells within the cancerous breast tissue that were able to recognise and target four mutant tumour proteins.
Women with early-stage breast cancer tend to have high survival rates, but their case worsens drastically if the cancer returns to other parts of the body.
"Patients really struggle having to make that decision, and now they don't have to". "We're saving people these side effects".
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Lead author Dr Joseph Sparano, of Montefiore Medical Centre in NY, said: "Any women with early stage breast cancer 75 or younger should have the test and discuss the results of TAILORx with her doctor". "I eat healthy. What?'" said Robyn Tuttle, who is now cancer free.
After enrolling for new trial in 2015, doctors in the U.S. adopted an experimental approach combining two different forms of immunotherapy after conventional hormone treatments and chemotherapy failed.
The results show that all women over 50 with a recurrence score of 0 to 25 can be spared chemotherapy and its toxic side effects.
The Oncotype DX genetic test has been available on the NHS since 2013, but the National Institute for Health and Care Excellence (Nice) is now updating its guidance on whether it should be recommended for use. Generally, after surgery, such patients receive endocrine therapy, such as tamoxifen, which is created to block the cancer-spurring effects of hormones.
Because of her work as a nurse, she was familiar with chemotherapy's sometimes harsh effects.
The patient, 52-year-old Judy Perkins, was first diagnosed with breast cancer in 2003.
While much more study is needed, researchers say because all cancers have mutations, this approach could potentially be used to treat many different types of cancer. Breast cancer remains the second most common cause of death from cancer among females in Australia. Rates for freedom from disease recurrence at a distant site were also similar, at 94.5% and 95% for the endocrine therapy and chemoendocrine therapy groups, respectively, as were rates for freedom from disease at a distant or local-regional site (92.2% and 92.9%, respectively) and for overall survival (93.9% vs 93.8%.).
This is the largest study ever done on breast cancer treatment. Data on premenopausal women and those younger than 50 who scored at the higher end of the intermediate-risk range, 16 to 25, was analyzed separately. Doctors do say chemotherapy is still effective and necessary in treating certain patients.